Iron-based sintered compact and method for production thereof

ABSTRACT

Provided is an iron-based sintered body with a rustproof function comprising a layer containing 0.01 to 5 at % of indium on the surface of the iron-based sintered body, or an iron-based sintered body with a rustproof function containing 0.01 to 5 at % of indium throughout the sintered body, and the iron-based sintered body having iron as its principal component is manufactured by performing sintering in a gas atmosphere containing indium vapor or indium. Thereby obtained is an iron-based sintered body, as well as the manufacturing method thereof, capable of easily improving the rustproof effect without having to hardly change the conventional process.

TECHNICAL FIELD

The present invention pertains to mixed powder for powder metallurgy tobe employed in the manufacture of sintered components, brushes and soon, and particularly to an iron-based sintered body suitable inmanufacturing the likes of iron-based sintered components superior inrustproof performance to be used as a solid lubricant or the like, andthe manufacturing method thereof.

BACKGROUND ART

Generally, iron powder used in the application of sintered mechanicalcomponents, sintered oil retaining bearings, metal graphite brushes andso on rusts easily, and is commonly used upon mixing an organicrust-prevention agent such as benzotriazole therein.

Nevertheless, although such an organic rust-prevention agent possesses atemporary rustproof effect, it decomposes or evaporates at 500° C. orhigher, and becomes lost at an ordinarily employed sintering temperatureof 700° C. or higher. Therefore, the same condition will occur unlessrust prevention is performed after the sintering, and there is a problemin that the sintered object will rust easily.

Meanwhile, in order to obtain the rustproof performance after sintering,a proposal has been made to form a composite powder sintered body bymixing a slight amount of metal powder such as zinc, bismuth, lead orthe like With sintering powder having iron as its principal component.

However, this requires an additional step, the manufacturing processwill become complex as a result thereof, and there is a problem in thatthere will be variations in the quality all that much more. Further,even if metal powder of bismuth or lead is mixed in, minute particlesare merely dispersed, and it could not be said that it is evenlydistributed.

As a conventional additive agent for powder metallurgy, there is anadditive agent having organic acid cobalt metallic soap as itscomponent, and technology for manufacturing a sintered body by addingand mixing this additive agent 0.1 to 2.0% by weight, and then moldingand sintering this mixed powder has been disclosed (c.f. Japanese PatentLaid-Open Publication No. H10-46201).

Moreover, technology of adding and mixing metal stearate to rareearth-iron-boron permanent magnet coarse powder, which is mainlycomposed in atomic % of rare earth element R (among rare-earth elementscontaining Y, one or two or more elements are combined) of 10 to 25%,boron B of 1 to 12%, and the remaining part consisting of iron Fe (apart of Fe is replaced at least with one or more kinds of elementsselected from Co, Ni, Al, Nb, Ti, W, Mo, V, Ga, Zn and Si in a range of0 to 15%, if necessary), and thereafter dry-pulverizing this mixture hasalso been disclosed (c.f. Japanese Patent Laid-Open Publication No.H6-290919).

Further, a molding improving agent of alloy powder for a permanentmagnet consisting of at least one kind selected from polyoxyethylenealkyl ether, polyoxyethylene monofatty acid ester and polyoxyethylenealkylallylether compounded with at least on kind of stearate at 1/20 to5/1 compounding ratio has also been disclosed (c.f. Japanese PatentLaid-Open Publication No. S61-34101).

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an iron-based sinteredbody, as well as the manufacturing method thereof, capable of easilyimproving the rust-prevention effect without having to hardly change theconventional process.

As a result of intense study to resolve the foregoing problems, thepresent inventors discovered that the rust-prevention effect of productsafter sintering could be significantly improved by making indium existat least on the surface of the sintered body.

Based on this discovery, the present invention provides:

-   1. An iron-based sintered body with a rustproof function,    characterized in comprising a layer containing 0.01 to 5at % of    indium on the surface of the iron-based sintered body;-   2. An iron-based sintered body with a rustproof function    characterized in containing 0.01 to 5at % of indium throughout the    sintered body; and-   3. A manufacturing method of an iron-based sintered body having iron    as its principal component, characterized in that sintering is    performed in a gas atmosphere containing indium vapor or indium.

MODE FOR CARRYING OUT THE INVENTION

In order to improve the rustproof effect of the iron-based sintered bodyaccording to the present invention, the present inventors focusedattention on zinc stearate to be added in a slight amount as a lubricantupon forming powder.

Nevertheless, this zinc stearate has a problem in that it dissipatesduring sintering, and damages the sintering furnace since it has highcorrosiveness, and it has become evident that the rustproof effect ishardly any different from a case when it is additive-free.

As described above, in most cases, this zinc stearate is merely used asa lubricant upon molding, and is insufficient as a material forobtaining a high rustproof effect.

Here, in order to improve the rustproof effect even after sintering, ithas become clear that as a result of sintering iron-based materialpowder in a gas atmosphere containing indium such as indium vapor orindium suboxide (In₂O), the rustproof function can be significantlyimproved by at least forming a layer containing 0.01 to 5 at % of indiumon the surface of the iron-based sintered body, or including 0.01 to 5at % of indium throughout the sintered body.

This rustproof effect is effective even with a slight amount of 0.01 at% or more. Although the rustproof effect can be expected with indium of5 at % or more, the effect will be saturated, and further addition willbe a waste. Thus, it is desirable to contain 0.01 to 5 at % of indium.

As the gas containing indium, compounds such as indium suboxide (In₂O)that decomposes with the heat of sintering may be used.

With this type of a sintered body containing 0.01 to 5 at % of indium,in order to increase the function as a molding lubricant, sintering maybe performed upon adding metallic soap such as zinc stearate to thepowder for powder metallurgy.

Particularly desirable is metallic soap of low-temperature volatilemetal, and indium soap, bismuth soap, nickel soap, cobalt soap, coppersoap, manganese soap and aluminum soap may be used as suchlow-temperature volatile metal.

Not only do these metals function as a molding lubricant, they are alsocapable of increasing the rustproof effect. Needless to say, indium soapis able to obtain extremely superior rustproof effect and lubricanteffect.

Moreover, metallic soaps such as metallic soap stearate, metallic soappropionate and metallic soap naphthenate may be used as the soap.

As a result, the rustproof effect of sintered bodies can be improvedexponentially without having to significantly change the conventionalmanufacturing process of a sintered body.

Generally, it is desirable to add 0.1 to 2.0 parts by weight of suchmetallic soap to 100 parts by weight of metallic powder for powdermetallurgy having iron as its principal component.

Nevertheless, this additive amount may be changed in accordance with thetype of sintered body, and the additive amount does not necessarily haveto be limited to the foregoing additive amount. In other words, theadditive amount may be arbitrarily set within a range that is capable ofmaintaining the characteristics of the target sintered body.

The condition for improving the rustproof effect is that the surface ofthe iron-based sintered body comprises a layer containing 0.01 to 5 at %of indium.

EXAMPLES AND COMPARATIVE EXAMPLES

Next, the present invention is described based on the Examples. TheExamples are for facilitating the understanding of the invention, andthe present invention is not in any way limited thereby. In other words,the present invention covers other Examples and modifications based onthe technical spirit of the invention.

Example 1

1.0 wt % of graphite powder was mixed with iron powder (Hoganas reducediron powder). This mixed powder (fill of 1.5 to 2.5 g) was molded into atest piece of approximately 10.06 mmø×2.70 to 4.55 mmH under a moldingpressure of 6 t/cm².

The compact molded into this test piece was sintered in a batch typeatmospheric furnace at a sintering temperature of 1150° C., sinteringtime of 60 min., with indium vapor introduced therein, and under ahydrogen gas atmosphere. 0.05 at % of indium was contained in theoutermost surface portion of the sintered body after sintering.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 1. TABLE1 Indium content in Oxidation Resistance surface After 96 After 168After 336 layer Hours Hours Hours Example 1  0.05 at % No change inSlight change Slight change color in color in color Example 2  0.1 at %No change in Slight change Slight change color in color in color Example3  0.5 at % No change in Slight change Slight change color in color incolor Example 4    1 at % No change in Slight change Slight change colorin color in color Example 5    3 at % No change in Slight change Slightchange color in color in color Example 6    5 at % No change in Slightchange Slight change color in color in color Example 7  0.05 at % Nochange in Slight change Slight change color in color in colorComparative    0 at % Severe Severe change Severe change Example 1change in in color in color color Comparative    0 at % Severe Severechange Severe change Example 2 change in in color in color colorComparative 0.005 at % Some change Severe change Severe change Example 3in color in color in color

Examples 2 to 6

Under the same conditions, sintered bodies were prepared in which theindium content contained in the surface portion was changed to 0.1 at %,0.5 at %, 1 at %, 3 at % and 5 at %, these sintered bodies were setinside a constant temperature and humidity chamber, and an atmosphericexposure test was conducted for 336 hours at a temperature of 40° C. andhumidity of 95% in order to conduct a moisture and oxidation resistanceexperiment. The results of the moisture and oxidation resistanceexperiment are shown in Table 1.

Comparative Example 1

Zinc stearate SZ-2000 (manufactured by Sakai Chemical Industry Co.,Ltd.) was used, and 0.8 wt % of this zinc stearate and 1.0 wt % ofgraphite powder were mixed with the iron powder. This mixed powder (fillof 1.5 to 2.5 g) was molded into a test piece of approximately 10.04mmø×2.73 to 4.58 mmH under a molding pressure of 6 t/cm².

The compact molded into this test piece was sintered in a batch typeatmospheric furnace at a sintering temperature of 1150° C., sinteringtime of 60 min., and under a hydrogen gas atmosphere.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 1.

Comparative Example 2

1.0 wt % of graphite powder was mixed with iron powder (Hoganas reducediron powder). This mixed powder (fill of 1.5 to 2.5 g) was molded into atest piece of approximately 10.06 mmø×2.70 to 4.55 mmH under a moldingpressure of 6 t/cm².

The compact molded into this test piece was sintered in a batch typeatmospheric furnace at a sintering temperature of 1150° C., sinteringtime of 60 min., without indium vapor introduced therein, and under ahydrogen gas atmosphere. An indium layer did not exist in surface of thesintered body.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 1.

Comparative Example 3

Similarly, 1.0 wt % of graphite powder was mixed with iron powder(Hoganas reduced iron powder). This mixed powder (fill of 1.5 to 2.5 g)was molded into a test piece of approximately 10.06 mmø×2.70 to 4.55 mmHunder a molding pressure of 6 t/cm².

The compact molded into this test piece was sintered in a batch typeatmospheric furnace at a sintering temperature of 1150° C., sinteringtime of 60 min., with a slight amount of indium vapor introducedtherein, and under a hydrogen gas atmosphere. 0.005 at % of indium wascontained in the outermost surface portion of the sintered body aftersintering.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 1.

Example 7

Synthesized indium stearate (In content of 12.0 wt %) was pulverized,and this was put through a sieve to obtain fine powder of 250 meshes orless.

0.8 wt % of this indium stearate (abbreviated as “In” in Table 1 above)and 1.0 wt % wt of graphite powder were mixed with the iron powder(Hoganas reduced iron powder). This mixed powder (fill of 1.5 to 2.5 g)was molded into a test piece of approximately 10.06 mmø×2.70 to 4.55 mmHunder a molding pressure of 6 t/cm².

The compact molded into this test piece was sintered in a batch typeatmospheric furnace at a sintering temperature of 1150° C., sinteringtime of 60 min., with indium vapor introduced therein, and under ahydrogen gas atmosphere. 0.05 at % of indium was contained in theoutermost surface portion of the sintered body after sintering.

This sintered body was set inside a constant temperature and humiditychamber, and an atmospheric exposure test was conducted for 336 hours ata temperature of 40° C. and humidity of 95% in order to conduct amoisture and oxidation resistance experiment. The results of themoisture and oxidation resistance experiment are shown in Table 1.

The moldability of the sintered body according to the present Examplewas extremely favorable since it is using indium stearate.

Likewise, results similar as Example 7 could be obtained in cases wheresoaps such as bismuth stearate (Bi content of 12.0 wt %), nickelstearate (Ni content of 12.0 wt %), cobalt stearate (Co content of 12.0wt %), copper stearate (Cu content of 12.0 wt %), manganese stearate (Mncontent of 12.0 wt %) or the compounds thereof were added to the ironpowder (Hoganas reduced iron powder).

Next, as evident from Table 1, regarding Comparative Examples 1 to 3 inwhich a lubricant was not added to the iron powder, in the moistureresistance and oxidation resistance experiment after sintering, changein color (corrosion) occurred after 96 hours (4 days), and, togetherwith the lapse in time, the degree of change in color increasedgradually. The change in color was severe after 336 hours.

Meanwhile, with Examples 1 to 7 according to the present invention, itis clear that each of the Examples only has a slight change in colorfrom the foregoing moisture resistance and oxidation resistanceexperiment after the lapse of 336 hours, and each of such Examples hasmoisture resistance and oxidation resistance properties.

Accordingly, it has been confirmed that the sintered body of the presentinvention containing a prescribed amount of indium in the surfaceportion thereof has favorable moisture resistance and oxidationresistance properties. Further, the moldability was favorable when usingmixed powder for powder metallurgy to which metallic soap was addedthereto, and the obtained result was that the corrosion resistanceimproved even more.

EFFECT OF THE INVENTION

As described above, the present invention provides an iron-basedsintered body, as well as the manufacturing method thereof, capable ofeasily and exponentially improving the rustproof effect without havingto significantly change the conventional manufacturing process of asintered body, and the rustproof effect of sintered bodies such assintered mechanical components, sintered oil retaining bearings, metalgraphite brushes and so on can thereby be improved remarkably.

1. An iron-based sintered body with a rustproof function, characterizedin comprising a layer containing 0.01 to 5 at % of indium on the surfaceof the iron-based sintered body.
 2. (deleted)
 3. A manufacturing methodof an iron-based sintered body having iron as its principal component,characterized in that sintering is performed in a gas atmospherecontaining indium vapor or indium.